Prior to this invention, the catalyst in oven heat exchanger systems did not react with a substantial portion of the effluent gases leaving the oven because the effluent flow over the catalyst was turbulent and unevenly distributed. This resulted in a higher energy cost in operating the oven, as less heat was transferred by the heat exchanger to ambient air entering the oven. In addition, quantities of unoxidized oven effluent gases were vented into the atmosphere. The invention improves the operation of the catalyst by creating a laminar, evenly distributed flow of effluent gases before the effluent gases contact the catalyst. The uniform and laminar flow increases the efficiency by which the catalyst oxidizes hydrocarbons and other oxidizable effluents, as more effluents can react with the catalyst when the flow is laminar and evenly distributed than when the flow is turbulent.
In the preferred embodiment of the invention, effluent gases are received from the oven and through a filter by a plug fan. The plug fan pushes filtered effluent gases into a heating chamber where the effluent gases are heated. The burner used in the heating chamber may incorporate flame spreaders to more evenly distribute the heat and avoid direct impingement of flame against the duct walls. Heated effluent gases exiting the heating chamber are received through a damper which allows heated effluents from the heating chamber to be vented directly into the atmosphere when desired (which would be done only during start up of the oven or under conditions where the heated effluent gases are safe to vent to the atmosphere). Heated oven effluent leaving the damper, when not vented to atmosphere, enter an elbow duct in which a plurality of spaced arcuate vanes are located. The arcuate vanes are located inside the elbow duct in such a way so that a vertical plane normally intersecting the vertical projections of the inside and outside curvature corresponding to the bend of the elbow duct would normally intersect the vertical projection of the arcuate vanes. In addition, the arcuate vanes are further located in the elbow duct in such a way as to normally deflect heated effluent gases entering the elbow duct to the opposing end of the elbow duct. Heated effluent gases leaving the elbow duct, which are now substantially laminar in flow, enter a perforated plate. The pressure drop occurring across the perforated plate tends to cause the effluent gas flow to be uniformly distributed before reacting with the heater catalyst. The heater catalyst oxidizes the hydrocarbons and other oxidizable substances in the effluent gases, which increases the temperature of the effluents and reduces the hydrocarbons to CO.sub.2 and H.sub.2 O. The oxidized effluents then enter the hot side of the heat exchanger. The heat exchanger transfers the heat generated from oxidizing effluent gases to ambient air entering the cold chamber of the heat exchanger. The oxidized effluent gases exiting the hot chamber of the heat exchanger are then vented to atmosphere.
Ambient air enters the oven heat exchanger system through a filter which removes particulates. The ambient air is then received through a damper which controls the amount of filtered ambient air entering the cold chamber of the heat exchanger. As the filtered ambient air passes through the cold chamber of the heat exchanger, heat is transferred from the oxidized oven effluent entering the hot chamber of the heat exchanger to the ambient air. The heated ambient air exiting the cold chamber of the heat exchanger is then mixed with oven effluents which are received directly from the oven. The mixed oven effluent and the heated ambient air is then received through a filter into a second heating chamber. The burner used to heat the mixed oven effluent and heated ambient air many incorporate flame spreaders to evenly distribute the heat and avoid impingement of the flame against the duct walls. The burner operates intermittently to raise the temperature of the mixed effluents and heated ambient air to the level required for the particular painting process employed before the mixture is recirculated to the oven by a plug fan.